Memory and the Hippocampus Notes

Memory and the Hippocampus

Definitions

  • Autobiographical memory:
    • Recall of specific past events with time, place, and personal involvement.
  • Semantic memory:
    • General knowledge and facts.
  • Hippocampus:
    • Elongated structure in the medial temporal lobe, subdivided into distinct cell-type regions.
  • Patient H.M.
    • Surgery to reduce epileptic seizures.
    • Removal of the medial temporal lobe, including the hippocampus.
  • Results:
    • Inability to recall new personal experiences (autobiographical memories).
    • Intact IQ, language, working, procedural, and semantic memory (pre-lesion).
  • fMRI evidence:
    • Hippocampal activity predicts whether items will be remembered or forgotten.
    • Strong activation during retrieval of events.

Encoding New Memories

  • Binding separate cortical representations into a coherent whole.
  • Cellular level à plasticity via long term potentiation (LTP).
  • Neural oscillations:
    • Provide temporal windows for neural firing and shape synaptic plasticity.
    • Hippocampal theta rhythm (3-8 Hz) linked with navigation and memory encoding.

Remote Memory Storage Debate

  • Conflicting evidence on the hippocampus' role in recalling older autobiographical memories.
  • Standard Consolidation Theory:
    • Autobiographical memories become independent of the hippocampus as they age due to system-level consolidation.
  • Multiple Trace Theory:
    • Memory traces are cumulatively stored in the hippocampus.
    • The hippocampus has a perpetual role in memory retrieval and storage.

Resolving the Debate

  • fMRI consistently shows hippocampal activation during autobiographical memory recall.
  • Longitudinal evidence:
    • The hippocampus is equally involved in both recent and remote memories.
  • Hippocampus is not a permanent storage site; neural structures are renewed.

Beyond Autobiographical Memory

  • Hippocampus's role in other cognitive processes.
  • Ventromedial prefrontal cortex (vmPFC) is involved in autobiographical memory recall.
    Imagining atemporal scenes activates the hippocampus.
  • Future thinking evokes similar brain regions as memory recall.
  • The hippocampus is involved in complex navigation.

Scene Construction Theory

  • Mental construction of scene imagery is a key process that autobiographical memory, future thinking, and spatial navigation have in common.
  • Scenes are used to build models of the world.
  • Autobiographical memory recall involves reconstructing event information in the form of scene visual imagery facilitated by the hippocampus.